a definite nose down pitch change (at 0:13) just before the flare. Is this significant? And why would a pilot do this at this stage of the approach?
Perhaps they got "smacked" in the face by a strong gust and the reaction was to counter by pushing forward; I would probably do the same (not to the same extent though, hopefully). A big gust at that stage, causing a jump in speed which if left uncorrected could result in a big balloon and long/hard "drop it on" landing.
His nose down pitch attitude at 100ft suggests maybe he was carrying excess speed.
I don't fly the 767, but my little Boeing requires all of the gust to be added to Vref. That would be Vref + 13 in this case (from that METAR). That would flatten out the deck angle. If the earlier description of the (atrocious) conditions is correct, they may have been carrying maximum additives.